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encode_residual_fixed(): replace FIR with finite differences.

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4x faster order 2, 3.5x order 3, 3x order 4.
overall flac encoding: 35% faster at compression_levels 0-2, no effect at higher levels.

Originally committed as revision 10624 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Loren Merritt 2007-09-29 23:21:57 +00:00
parent 0b04ebb326
commit a309dce75f
1 changed files with 27 additions and 6 deletions
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33
libavcodec/flacenc.c
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@ -840,14 +840,35 @@ static void encode_residual_fixed(int32_t *res, const int32_t *smp, int n,
for(i=order; i<n; i++)
res[i]= smp[i] - smp[i-1];
}else if(order==2){
for(i=order; i<n; i++)
res[i]= smp[i] - 2*smp[i-1] + smp[i-2];
int a = smp[order-1] - smp[order-2];
for(i=order; i<n; i++) {
int b = smp[i] - smp[i-1];
res[i]= b - a;
a = b;
}
}else if(order==3){
for(i=order; i<n; i++)
res[i]= smp[i] - 3*smp[i-1] + 3*smp[i-2] - smp[i-3];
int a = smp[order-1] - smp[order-2];
int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
for(i=order; i<n; i++) {
int b = smp[i] - smp[i-1];
int d = b - a;
res[i]= d - c;
a = b;
c = d;
}
}else{
for(i=order; i<n; i++)
res[i]= smp[i] - 4*smp[i-1] + 6*smp[i-2] - 4*smp[i-3] + smp[i-4];
int a = smp[order-1] - smp[order-2];
int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
int e = smp[order-1] - 3*smp[order-2] + 3*smp[order-3] - smp[order-4];
for(i=order; i<n; i++) {
int b = smp[i] - smp[i-1];
int d = b - a;
int f = d - c;
res[i]= f - e;
a = b;
c = d;
e = f;
}
}
}